(a) Technical Field
The present invention relates to a system for detecting a pin hole in a fuel cell stack part. More particularly, it relates to a device and a method for accurately detecting the presence of pin holes in fuel cell stack parts for ensuring quality of the fuel cell stack.
(b) Background Art
A fuel cell stack is typically manufactured by alternately stacking hundreds or more of five-layered membrane-electrode assemblies having a gas diffusion layer on both sides of three-layered membrane-electrode assemblies and metal (or graphite) separators.
In particular, the membrane electrode assemblies (MEA) and gas diffusion layers are bonded together to form a five-layered structure, before the stack is manufactured, to improve productivity of the fuel cell stack. Here, the carbon fibers constituting the gas diffusion layers may bore or permeate the polymer electrolyte membrane layers of the membrane electrode assemblies (MEA) such that pin holes may be formed in the above bored or permeated portions. In the case of a separator, it is highly likely that pin holes are formed during a pressing process for the manufacture of a single product.
Further, in the fuel cell stack, when deterioration of the entire polymer electrolyte membranes is not uniform, pin holes may be formed in deteriorated portions, thereby damaging the corresponding cells and terminating the lifespan of the entire stack.
Therefore, when a part with pin holes is used in manufacturing a fuel cell stack, the output performance and durability of the stack are considerably influenced. Accordingly, when a fuel cell vehicle equipped with the stack travels, a pin hole is formed in any one of the hundreds of membrane electrode assemblies and/or separators, and the operation of the vehicle is shut down. Therefore, it is essential to check for the presence of pin holes in each part before the manufacture and assembly of the fuel cell stack.
As an example of a conventional technique for examining pin holes in the related art, Korean Patent No. 10-0053351 discloses an optical apparatus for the detection of holes, in which a photoelectric light receiver is disposed on the same side as a laser scanner and receives light reflected from a scan line. A second laser scanner is also disposed in a limited space (i.e., A) in front of a web from a first laser scanner at the opposite side to the web and scans the other side of the web in the limited space A, using a scan line parallel with a first scan line. Another linear photoelectric light receiver extends in parallel with a second scan line and sends an electric signal to an electronic process circuit after receiving light reflected from the second scan line. Electric signals transmitted to the electronic process circuit from the two photoelectric light receivers come in connection with an intermediate storage device which is stores a first received signal. Then a pin hole signal is transmitted, when the same signals are generated from the same positions of the webs of both light receivers.
However, the above apparatus cannot measure the parts of a multi-layered fuel stack because it can only be applied to single-layered webs. Thus, it is limited when measuring the parts with a laser scanner and a light receiver, because the shapes of pin holes generated in a porous three-layered or five-layered MEA or separator, which has a multi-layered structure as a part of a fuel cell stack, do not have linearity.
Further, it is not possible to apply the above apparatus to the parts of a fuel cell stack by conveying a roll type object, such that MEAs (three-layered or five-layered) and separators which are the parts of the fuel cell stack cannot be continuously conveyed through bias rollers, because they need a certain degree of flatness in a quadrangular sheet type, and accordingly, the parts of the fuel cell are destroyed by rolling.
Another example of related art appears in Korean Patent No. 10-0878400 which discloses a pin hole detector, in which light passing through a pin hole, in the z-axis direction, is combined with a photo detector. Since the traveling direction of noise light, except for the light passing through the pin hole is inclined with respect to z-axis, a combination of the noise light with the photo detector is limited by a first and second optical means that limits the incident angle.
However, the apparatus cannot measure the parts of a multi-layered fuel stack because it can only be applied to metal or resin film. That is, it is limited in measuring the parts with an optical scanner and a light receiver, because the shapes of pin holes generated in a porous three-layered or five-layered MEA or separator, which has a multi-layered structure as a part of a fuel cell stack, do not have any linearity.
As another example, Korean Patent Application No. 10-2002-0084521 discloses a pin hole detector that detects a pin hole in a thin plate material, such as a steel plate, and includes a laser light source that generates a laser line beam with a single wavelength, a first cylindrical lens that converts a line beam from the laser light source into parallel light, a second cylindrical lens that collects the parallel light, an APD (Avalanche Photo Diode) sensor that is disposed at the focus of the second cylindrical lens, and a signal processor that determines the presence of a pin hole based on the output from the APD sensor.
However, this apparatus can only be applied to single layered metals but not to parts such as a multi-layered fuel cell stack. The pin holes generated in a porous three-layered or five-layered MEA or separator, which has a multi-layered structure as a part of a fuel cell stack, do not always have linearity, and thus the measurement using the laser line beam and the APD sensor is limited.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.